Fans of "Dr. Horrible's Sing-a-Long Blog" were thrilled this fall to learn that its creator, Joss Whedon, would direct an upcoming episode of "Glee" -- but the story just got even more awesome: Michael Ausiello reports that Whedon's episode will also feature an extremely special guest star: Neil Patrick Harris (seen above headlining a musical number at his day job). And when you think about it, we probably should have predicted this: not only did Harris and Whedon collaborate on the aforementioned "Horrible" (in which Harris played the titular doctor), but Harris is just the latest Broadway star to land in Lima: Kristin Chenoweth already appeared in Episode 5, while her "Wicked" co-star Idina Menzel is set to appear in the back nine episodes as the coach of McKinley's sworn rivals, Vocal Adrenaline. Olivia Newton-John is scheduled. Jennifer Lopez may share an episode with Madonna. Since there is apparently no one in Hollywood who could stand to refuse an offer, we decided to make our own wish list.

1. Megan Mullally. In case we had forgotten her peerless comic chops in the years since "Will & Grace" went off the air, this season Mullally returned to sitcoms with an amazing guest role on "Parks & Recreation" opposite her real-life husband, Nick "Ron Swanson" Offerman.

But Mullally is not only funny, she can also sing: the Broadway vet has released albums with her band, Supreme Music Program, and played a vocal coach in last September's remake of "Fame," in one memorable scene favoring her students with a karaoke number. Mullally also has a tie to "Glee": she's been tapped to replace Jane Lynch on the Starz sitcom "Party Down." And if a role on the show keeps her out of future TV ads for I Can't Believe It's Not Butter, surely we can all agree that's worth it. Her former alter ego, Karen Walker, was interested in fashion; maybe she could play McKinley's Home Ec teacher for a cover of "Dress You Up" in a sequel to the Madonna episode.

2. Kerry Butler. I realize hers isn't exactly a household name, but the adorable Butler absolutely slayed me in the recent (tragically closed) Broadway adaptation of "Xanadu." And what do you know -- before that, she originated the role of Penny Pingleton in Broadway's "Hairspray," in a cast that also featured a Link Larkin played by...Matthew Morrison. Butler is currently on Broadway as the female lead in "Rock of Ages," which means the jukebox musical is a form with which she's already quite comfortable. Plus: voice of an angel.

I don't know the plot of the episode in which Newton-John will appear, but if someone just writes in a flashback for her character, there's Butler cast: after doing it in eight shows a week for a matter of months, Butler already knows how to play a young Newton-John.

3. Taye Diggs. Well, this one is a no-brainer. Diggs has not only appeared on Broadway in the original cast of "Rent" -- it happens to be where he met his wife...Idina Menzel. Also, Audra McDonald -- who plays his ex-wife on "Private Practice" -- starred in the original cast of "Ragtime" with...Lea Michele. So they can probably get him. He can sing. He can act. He can look good.

Have we met Mercedes's dad yet? Maybe we should, and maybe he should be Taye Diggs.

4. Ed Helms. It's obvious, isn't it? Helms has already co-starred with Kevin McHale in an episode of "The Office" -- McHale played the pizza delivery boy Michael kidnapped and left trapped in the conference room. And Helms loves to sing...

It's no accident that his "Office" character, Andy Bernard, is the former member of a college a cappella group called "Here Comes Treble." Put some chunky glasses on that dude and he could play Artie's father in a second.

5. Bill Murray. Obviously, singing is not a problem for this guy.

Bill Murray singing ‘Star Wars’ on SNL from http://jackyan.vox.com/

He and Stephen "Sandy Ryerson" Tobolowsky already appeared together in "Groundhog Day." And as for making crazy cameos...well, we all learned last year that he's open to them. School Superintendent Bill Murray has to crack down on Principal Figgins...in song? Make it happen, Ryan Murphy.